Because Android phones area so similar in capability, each manufacturer has an incentive to release models (often with relatively minor improvements), often. If you were to go into a store, and didn't know jack about phones or operating systems, the idea of buying a phone that's been out on the market for six months, versus one that was released just recently, might factor into your decision.

I don't know how the handset makers are going to get away from this. Ultimately, HTC, Samsung, et. al. are selling what's 95% the same thing. Skinned differently (maybe), but largely the same thing. I would expect Windows Phone handsets to have the same issue. Maybe, as Samsung is doing, bundling additional services to differentiate yourself may distance themselves more from other handset makers.

Apple gets away from that by not having multiple, different implementations of the iPhone. By being a different enough product, consumers probably aren't comparing iPhones to Android phones in the same way they compare Android phones to each other. I'm not stating this is good or bad.

But the flip side is that Android manufacturers might have a dozen models capable of supporting an upgrade on the market. Verizon et. al might look at this problem as 12 handsets * 4 vendors = 48 tests * the cost to test a handset = too much money to be worth it. This may be especially true where a particular model didn't sell that well and there are relatively few units out there. So I would expect to see two handsets that were practically identical being treated differently based on whether one was a popular model. Apple, instead, has 3 handsets with a large user base.

So, ultimately it is the 'fault' of the carrier, even though I don't think fault is the right word. They're making decisions on what is the most economical way to handle their network and the devices on it. Maybe if they weren't such control freaks this wouldn't be a problem. Of course, if an update did get pushed out, and that caused one model of phone to miss-behave to the point that it effected your phone service, would you just shrug it off and say "hey, it's cool?"